This invention relates to the etching of aluminum capacitor foil using a pulsed direct current which falls to zero in the intervals between pulses. The duration of each pulse is at least nine times as long as the length of the interval and is preferably 3 to 27 milliseconds. The electrolyte is an aqueous solution of sodium chloride and sodium sulfate. The process is carried out at 50 to 90.degree. C. and at a pulse current density of 2 to 10 A/in.sup.2.
It is desirable to use pulsed direct current to etch aluminum foil for low voltage use, e.g., 0-100 V formations, because it gives a foil which has a higher capacitance than that obtainable with conventional direct current or alternating current etching for formation voltages in the above range and particularly for 60 V formation or lower.
It has been known to use direct current pulses to etch aluminum foil. Generally, the current does not drop to zero between pulses so there is always current flowing to the foil. When a pulsed current is used where the current does drop to zero, the pulse time is so short as to be impractical with the commercial power supplies presently available. Other pulsed processes involve the use of heavy metal salts which present disposal, if not toxicity, problems.